It was planned to investigate, in mice that received ACTH, the influence of Panax Ginseng upon DNA synthesis of submandibular gland by observing incorporation of [³H] thymidine into the tissue cells. Thirty male mice (body weight: 18 ~ 20 g) were divided equally into the ginseng-ACTIH and the saline-ACTH groups. Each animal of the ginseng-ACTH and the saline-ACTH groups received every day (subcutaneously) 0.05 m1/10 g body weight of ginseng extract(4 mg of ginseng alcohol extract in 1 ml of saline) and the same amount of saline, respectively, for 5 days. On the 5th experimental day, all animals received 0.01 unit of ACTH intraperitoneally one hour after the last medication, and 1 μCi/g body weight of [³H] thymidine after one more hour. Five animals, at a time, of each group were sacrificed 1, 10, and 24 hr after [³H] thymidine administration, and the radioactivity of cells in their mandibular gland was measured autoradiographically in terms of the % number of radioactive cells in 1,000 cell counts (Radioactive Index, R.1.). Results obtained were as follows: 1. The radioactive indices obtained from submandibular gland of the saline-ACTH group 1, 10 and 24 hr after [³H] thymidine administration were 15.2±0.32, 20.1±0.30, and 24.5±0.52(mean±S.D.) in the mucous cells, 13.0±0.22, 10.2±0.05, and 7.5±0.42 in the serous cells. and 10.5±0.40, 13.6±0.32, and 15.9±0.42 in the duct cells, while the mean±S.D. of the values obtained from the 3 cell types 1, 10 and 24 hr after [³H] thymidine were 10.9±0.28, 12.4±0.31, and 10.0±0.39. Thus the radioactive indices obtained from the ginseng-ACTH group were generally lower than those obtained from the saline-ACTH group. It is inferred from the above results that the ginseng tends to promote the suppressive action of ACTH upon DNA synthesis of cells in the mandibular gland.